This invention relates generally to nuclear reactors and, more particularly to apparatus for plugging openings or leaks in nuclear plant piping systems for maintenance or repair.
A typical boiling water reactor (BWR) includes a pressure vessel containing a nuclear fuel core immersed in circulating coolant water which removes heat from the nuclear fuel. The water is boiled to generate steam for driving a steam turbine-generator for generating electric power. The steam is then condensed and the water is returned to the pressure vessel in a closed loop system. Piping circuits carry steam to the turbines and carry recirculated water or feed-water back to the pressure vessel that contains the nuclear fuel.
Additional piping circuits perform emergency cooling of the core. Some of these piping systems are high pressure systems, others provide reactor cooling water at relatively lower pressures, still others are designed to supply cooling flow while the reactor is in a shutdown state and the pressure vessel is open. During shutdown conditions maintenance work is performed on reactor plant systems rendering some components inoperable in their normal mode. To accomplish maintenance work during shutdowns, alternate means of isolating piping systems and vents need to be provided. This can be accomplished by lowering the water level in the reactor below a level of the elevation of the equipment desired to be worked on. Depending on the elevation of the equipment, a significant disruption to reactor maintenance activities may be required. The isolation of equipment may require removable of all fuel from the reactor, installation of the reactor pressure vessel head, restriction of access or evacuation of the containment and drywell areas. After completion of the maintenance, the above steps must be reversed prior to returning to normal outage maintenance activities.